During the manufacture of printed circuit board (PCB) assemblies, testing is performed at one or more stages to ensure that the finished product functions adequately. In some manufacturing operations, printed circuit boards are first tested before any components are mounted to them. The components may be separately tested before they are attached to printed circuit boards (PCB), usually by soldering. Once the components are attached, a further test may be performed to verify that the components are properly attached. Such testing includes “opens” tests and “shorts” tests that indicate defects in attachment of contact points of the components to the circuit assembly. These contact points, and conducting structures within the component connected to those contact points, are generally referred to as “pins,” even though the contact points may take many shapes, including posts, gull wing leads or solder balls.
One approach to testing the connections to pins is called capacitive testing. In a capacitive “opens” test, a probe that includes a sense plate is pressed near or against a component with a pin to be tested. A test signal is generated at a point on the circuit assembly that should be connected to the pin under test in a properly manufactured circuit assembly. If the pin under test is properly connected to the circuit assembly, the test signal will propagate from the circuit assembly through the pin and corresponding conducting structures within the component. Though the probe plate is separated from those conducting structures, the test signal can capacitively couple to the probe plate. During a test, the signal received at the probe plate is analyzed to determine whether the test signal has been capacitively coupled to the probe plate, indicating that there is a good connection between the assembly and the pin of the component.
Though capacitive testing may be desirable, it has not been widely used for certain types of components. For example, miniature sockets and connectors have not been widely tested using capacitive test techniques. Sockets generally contain a cavity shaped to receive a semiconductor chip or other component. Each pin of the socket is formed at one end of a conductor. The other end of the conductor extends into the cavity and provides a spring contact to which other semiconductor chips can be connected. Similarly, dual-inline connectors contain two parallel rows of pins, with two corresponding parallel rows of conductors within the cavity to contact corresponding conductive members of a mating connector. While non-miniaturized components may be readily tested, when a miniature socket or connector is tested, there is little conductive structure in the component under test through which a test signal applied to a pin under test can couple to a probe plate, making capacitive testing of such components difficult.